Automatic generation of active coordinates for quantum dynamics calculations: Application to the dynamics of benzene photochemistry

Lasorne, Benjamin; Sicilia, Fabrizio; Bearpark, Michael J.; Robb, Michael A.; Worth, Graham A.; Blancafort, Lluı́s

doi:10.1063/1.2839607

Cited by 42 publications

(45 citation statements)

References 46 publications

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“…S 0 population decay pathway of PARA is similar to the one of styrene and other substituted benzenes, the reason for the long S 1 lifetime could be the rigidity of the paracyclophane cage structure, which restricts the out of plane motions of the benzene ring that lead to the S 1 /S 0 CI. [46][47][48]…”

Section: Discussionmentioning

confidence: 99%

Pseudo‐Bimolecular [2+2] Cycloaddition Studied by Time‐Resolved Photoelectron Spectroscopy

Brogaard

Boguslavskiy

Schalk

et al. 2011

Chemistry A European J

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The first study of pseudo‐bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time‐resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo‐gem‐divinyl[2.2]paracyclophane. From X‐ray crystal diffraction measurements we found that the ground‐state molecule can exist in two conformers; a reactive one in which the vinyl groups are immediately situated for [2+2] cycloaddition and a nonreactive conformer in which they point in opposite directions. From the measured S1 lifetimes we assigned a clear relation between the conformation and the excited‐state reactivity; the reactive conformer has a lifetime of 13 ps, populating the ground state through a conical intersection leading to [2+2] cycloaddition, whereas the nonreactive conformer has a lifetime of 400 ps. Ab initio calculations were performed to locate the relevant conical intersection (CI) and calculate an excited‐state [2+2] cycloaddition reaction path. The interpretation of the results is supported by experimental results on the similar but nonreactive pseudo‐para‐divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S1 state.

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Section: Discussionmentioning

confidence: 99%

Pseudo‐Bimolecular [2+2] Cycloaddition Studied by Time‐Resolved Photoelectron Spectroscopy

Brogaard

Boguslavskiy

Schalk

et al. 2011

Chemistry A European J

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“…In order to alleviate this issue, much recent work has focussed on so-called direct-dynamics (DD) methods whereby the PESs are generated "on-the-fly" as the nuclear dynamics proceeds [15,16]. In addition to the previously mentioned TSH method, the ab initio multiple spawning (AIMS) method [17][18][19][20] and the DD-variational multi-configuration Gaussian (DD-vMCG) [21][22][23][24][25][26] method have shown 70 much success in modelling non-adiabatic dynamics. AIMS uses a wavefunction formed of a linear combination of classically-evolving Gaussian functions with quantum mechanically-evolving coefficients, whilst the DD-vMCG method takes this a 75 step further by using quantum mechanical (rather than classical) propagation of Gaussians.…”

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confidence: 99%

Direct grid-based quantum dynamics on propagated diabatic potential energy surfaces

Richings

Habershon

2017

Chemical Physics Letters

100

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We present a method for performing non-adiabatic, grid-based nuclear quantum dynamics calculations using diabatic potential energy surfaces (PESs) generated "on-the-fly". Gaussian process regression is used to interpolate PESs by using electronic structure energies, calculated at points in configuration space determined by the nuclear dynamics, and diabatising the results using the propagation diabatisation method reported recently [J. Phys. Chem. A, 119, 12457 -12470 (2015)]. To test this new method, the nuclear dynamics on the ground and first electronic excited states of the butatriene cation is studied using a grid-based method. The evolution of diabatic state populations is in very good agreement with those produced using a fitted potential. Overall, our scheme offers a route towards accurate quantum dynamics on diabatic PESs learnt on-the-fly.Keywords: Direct-dynamics, Diabatisation, Grid-based quantum dynamics, Butatriene 2010 MSC: 00-01, 99-00The study of nuclear quantum dynamics of nuclei is of great importance in helping to understand of the time-evolution of molecular systems upon excitation of the electronic degrees-of-freedom (DOFs); such simulations can make direct connections to the states. [6,7] One can model these non-adiabatic transitions using classical mechanics, as in the trajectory surface hopping (TSH) algorithm, [2,[8][9][10] but as the dynamics are inherently quantum mechanical, it is better to use a quantum mechani-25 cal method such as the multi-configuration timedependent Hartree (MCTDH) approach [1, 11,12] where possible.The major bottleneck in performing quantum dynamics calculations is usually not the wavefunc-30 tion time-propagation, but the creation of an appropriate PES on which to run the dynamics. As quantum mechanics is non-local, one needs a PES which is known everywhere in the configuration space of the nuclear motion prior to running the 35 dynamics. For the fully quantum mechanical study of non-adiabatic systems it is usually necessary to convert the PESs from the adiabatic representation to a diabatic representation. The adiabatic representation of the potential is an energy-ordered set 40 of PESs, and corresponds to the energies generated by electronic structure programs. However, at points in configuration space where adiabatic surfaces become degenerate, such as at conical interePreprint submitted to Chemical Physics Letters December 20, 2016 sections (CIs), there is a discontinuity in the gradi-45 ent of the states, such that the adiabatic states are no longer smooth; furthermore, the coupling between the states at these points is also infinite. Neither property of the adiabatic PESs is conducive to performing wavepacket dynamics, so transforma-50 tion to the diabatic representation is performed, resulting in smoothly varying surfaces with finite couplings. Diabatic representations are not unique for a given set of adiabatic states, so an appropriate diabatisation scheme must be chosen before the 55 PES can be used in a dynamics calculation. PESs are usua...

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“…Related challenges are the following: developing robust diabatization methods for both kinds of quantum dynamics methods (see, e.g., Ref 145); generating active coordinates automatically for photochemical reactions in the context of reduced‐dimensionality techniques146; making second derivatives of the energy available in excited‐state quantum chemistry methods capable of dealing with dynamical correlation; developing less expensive excited‐state quantum chemistry methods such as CAS‐DFT (Complete Active Space Density Functional Theory)147; imbedding semiclassical and direct quantum dynamics in electronic structure codes148,149; developing new direct quantum dynamics approaches such as Bohmian trajectories150 and improving semiclassical treatments78,79,151; investigating larger‐scale problems (environment, complex structures such as chromophores in proteins, or organometal complexes) with hierarchical methods (hybrid quantum chemistry and quantum dynamics, effective coordinates115,152,153, and multilayer MCTDH154). …”

Section: Discussionmentioning

confidence: 99%

Excited‐state dynamics

Lasorne

Worth

Robb

2011

WIREs Comput Mol Sci

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Excited-state dynamics is the field of theoretical and physical chemistry devoted to simulating molecular processes induced upon UV-visible light absorption. This involves nuclear dynamics methods to determine the time evolution of the molecular geometry used in concert with electronic structure methods capable of computing electronic excited-state potential energy surfaces. Applications concern photochemistry (see Chapter CMS-030: Computational photochemistry) and electronic spectroscopy. Most of the work in this field looks at unsaturated organic molecules as these provide widely used chromophores with a straightforward photochemistry that can be described by a small number (usually two) of electronic states. The electronic ground state of closed-shell organic molecules is a singlet (electronic spin zero) termed S 0 . Molecules are promoted to their electronic excited states through absorption of UV-visible light (200-700 nm), usually to the first or second singlet, S 1 or S 2 . Typical examples are well represented as a one-electron transition from the π or n highest occupied molecular orbital to a π * or σ * low-lying unoccupied molecular orbital. The photo-excited system will deactivate and return to the electronic ground state over a timescale that can be as short as about 100 fs for ultrafast mechanisms. For example, the initial event of vision is a photo-isomerization of the retinal chromophore in the rhodopsine protein that occurs in ca. 200 fs. 1,2 The goal of a computational approach to the simulation of photo-induced processes is the complete description of what happens at the molecular level from the promotion to the excited electronic state to the formation of products or regeneration of reactants back in the electronic ground state.A fter light absorption, several photophysical or photochemical deactivation mechanisms can compete depending on their relative efficiencies. These are summarized in Figure 1, a typical Jablonski diagram. The excess energy can be released through light emission (fluorescence from a singlet or phosphorescence from a triplet) or through radiationless decay processes (internal conversion between singlets or intersystem crossing between a singlet and a triplet) that convert it into vibrational energy in S 0 . The spectral position, shape, and width of the absorption or emission spectra will depend on all the competing events that dominate the short-timescale dynamics of the molecule (changes in the molecular geometry through nuclear motion coupled to changes in

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Automatic generation of active coordinates for quantum dynamics calculations: Application to the dynamics of benzene photochemistry

Cited by 42 publications

References 46 publications

Pseudo‐Bimolecular [2+2] Cycloaddition Studied by Time‐Resolved Photoelectron Spectroscopy

Pseudo‐Bimolecular [2+2] Cycloaddition Studied by Time‐Resolved Photoelectron Spectroscopy

Direct grid-based quantum dynamics on propagated diabatic potential energy surfaces

Excited‐state dynamics

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